The serum estradiol/oocyte ratio in patients with breast cancer undergoing ovarian stimulation with letrozole and gonadotropins

Objective To investigate the patterns of estradiol-oocyte ratio (EOR) and estradiol-mature oocyte ratio (EMOR) in patients with breast cancer undergoing controlled ovarian stimulation (COS) using letrozole and gonadotropins for fertility preservation. Methods This retrospective study included 32 breast cancer patients underwent COS for fertility preservation and no patients had previously undergone gonadotoxic treatments. Basal characteristics and in vitro fertilization (IVF) outcomes were compared according to the age of women (age <35 vs. age ≥35) and the starting phase of ovarian stimulation (early follicular phase vs. late follicular phase vs. luteal phase). Results Patients who were administered with a letrozole-combined regimen, the peak serum estradiol (E2) was maintained at a low level (386.3±346.9 pg/mL). EOR was 52.4±78.8 pg/mL, and EMOR was 71.0±41.2 pg/mL. When the 2 groups were compared according to the age of women (age <35 vs. age ≥35), EOR was 34.5 (22.2-46.5) pg/mL and 40.7 (19.3-65.3) pg/mL, respectively; EMOR was 79.8 (40.8-90.6) pg/mL and 68.8 (44.5-85.9) pg/mL, respectively. There was no significant difference in the IVF outcomes. When the 2 groups were compared according to the starting phase of ovarian stimulation, there were no significant differences in IVF outcomes, EOR and EMOR among the groups. Conclusion Measuring the peak E2 concentration in breast cancer patients undergoing IVF for fertility preservation with a co-treatment of letrozole allows for the prediction of the numbers of oocytes and mature oocytes.